Disclosed in Japanese Patent Application Laid-Open No. Hei 7-145339 is a water based metallic lustrous color ink for a ballpoint pen which contains aluminum powder, natural polysaccharides, a water-soluble organic solvent and water and has a viscosity of 100 to 1500 poise and in which a ratio of a viscosity at 1 rpm to a viscosity at 10 rpm is 3.0 or more and in which a quality changes less even after storing over an extended period of time and a discharging property of the ink in a ball-rotating part of the tip of the ballpoint pen is good. Further, it is described therein that "in order to provide the line with a metallic lustrous color, aluminum powder as a colorant can be used in combination with known water-soluble dyes such as acidic dyes, basic dyes and direct dyes", but no specific examples are disclosed.
However, the ink described in preceding Japanese Patent Application Laid-Open No. Hei 7-145339 is made by blending 0.7 to 10 parts by weight of natural polysaccharides for thickening, 5 to 40 parts by weight of a water-soluble organic solvent and 2 to 15 parts by weight of aluminum powder. That is, consideration is given so that aluminum powder is prevented from settling by limiting the content of the natural polysaccharides for thickening, but sometimes the discharging amount is little and sometimes splitting (an amount of ink in a part where the ball contacts a paper face is so little as to cause the ink to stay only at both sides thereof and therefore the line looks two) is liable take place. Accordingly, the ink has a problem in terms of practical use.
Further, disclosed in Japanese Patent Application Laid-Open No. Hei 2-69580 is a low viscosity water based metallic color ink containing a resin emulsion, in which dispersed is a paste of an aluminum powder pigment of which surface is wetted with a solvent of a hydrocarbon mixed with an ester based wax for rust-prevention. Disclosed in Japanese Patent Application Laid-Open No. Hei 6-313142 is a water based metallic lustrous color ink using a water-soluble dye, in which the content of an inorganic salt has been set to 0.5% by weight or less. Disclosed in Japanese Patent Application Laid-Open No. Sho 63-95277 is a water based metallic color ink containing an aluminum powder pigment, an amphoteric compound, a resin emulsion, water, an organic pigment and a metallic soap. Disclosed in Japanese Patent Application Laid-Open No. Sho 58-80368 is a water based metallic color ink for writing instruments containing an aluminum powder pigment, an acrylic resin emulsion, a polyvinyl alcohol and/or cellulose based water-soluble resin and a water-dispersed type pigment.
Disclosed in Japanese Patent Application Laid-Open No. Hei 6-192610 is a water based ink composition for writing instruments containing an aluminum pigment, a water-soluble organic solvent and a perfluoroalkylphosphoric ester and/or a perfluoroalkyltrimethylammonium salt.
The ink disclosed in Japanese Patent Application Laid-Open No. Hei 6-313142 mentioned above reveals a colored metallic lustrous color by using a water-soluble dye as a colorant. However, a dye penetrates into fibers of paper when the viscosity is lower than that of the ink composition for a ballpoint pen shown in Example 2, so that the dye draws outlines around the lines of the metal powder pigment, or a colored metallic lustrous color having a sufficient intensity is not obtained, and therefore the lines tend to become drawn lines close to a silver color. When a water based colored metallic color ink was actually prepared by using aluminum powder in combination with corresponding amounts of a thickener and a colorant (yellow pigment), it was found that the ink presented a beautiful golden color and that in actual writing, a colored metallic color was developed on a paper face which scarcely absorbs an ink, such as coated paper. On the other hand, when writing was carried out on a normal paper face (absorbent paper), particularly a colored paper face (absorbent paper), it was found that a colored metallic lustrous color was displayed immediately after writing. However, there was a problem that the drawn lines were finally turned close to a silver color due to fading of the color which was supposed to be caused by settling of the yellow pigment. Considered as a method for solving this problem is the method of adding a large amount of a color pigment to raise a viscosity of the ink to thereby delay a settling rate of the pigment. However, there occurs a problem in terms of storage stability or there is a problem such that stable discharge of the ink from the pen tip cannot be obtained.
Further, inks for low viscosity markers and felt tip pens using pigments as colorants are disclosed in Japanese Patent Application Laid-Open No. Sho 58-80368, Japanese Patent Application Laid-Open No. Sho 63-95277 and Japanese Patent Application Laid-Open No. Hei 2-69580 each described above. Those inks contain resin emulsions also as an essential component. However, the emulsions are used for a principal purpose of providing the drawn lines with a sticking property. For this purpose, a film-forming emulsion is used and blended in a large amount.
However, when this film-forming emulsion is used for paint markers, which use a so-called porous pen core for a pen tip and a valve mechanism for an ink tank, and which are capable of supplying a lot of an ink to the pen core at any time, there are scarcely problems. However, when it is used particularly for a ballpoint pen, a water based ballpoint pen in which a space of a flow pass in a ball tip part is small have easily a reduction in a flowing amount due to dry up at the pen tip and inferior writing because of a film-forming effect of the emulsion.
Further, it is described that the ink shown in Japanese Patent Application Laid-Open No. Hei 6-192610 described above can use known water-soluble dyes, organic pigments and inorganic pigments, but no specific examples are disclosed.
Accordingly, an object of the present invention is to provide a water based ink having a metallic luster for a ballpoint pen using aluminum powder blended with a thickener in a suitable amount, in which a reduction in the flowing amount and splitting are not brought about.
Further, an object of the present invention is to provide a water based pigment ink having a metallic lustrous color for a ballpoint pen containing aluminum powder and water-soluble organic solvent, in which a metallic lustrous color having good color development of the pigment is obtained as well in writing on an absorbent paper usually used, particularly a colored absorbent paper and beautiful lines can be drawn and in which a reduction in the flowing amount of the ink is scarcely brought about.